I 



' 




Book ' El^j- 



I 



epare;tc Bot^ 



PROCEEDINGS 

OF THE 

WASHINGTON ACADEMY OF SCIENCES 

Vol. IV, pp. 533-548. plates xxxii-xxxiv. SEPTEMBER 30, 1902. 



THE EYES OF RHINEURA FLORIDANA. 



BY 



CARL H. EIGENMANN. 
Professor of Zoology, Indiana University. 



WASHINGTON, D. C. 

Published by the Academy 

1902 



PROCKKDIKOS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 

Vol. IV, pp. 533-548. [Plates xxxii-xxxiv.] September 30, 1902. 



THE EYES OF RHINEURA FLORIDANA. 

By Carl H. Eigenmann. 

Professor of Zoology, Indiana University, 

CONTENTS. 

Introduction 533 

Habits of Rhineura c 534 

General Account of the Eye 535 

Minute Anatomy of the Eye 537 

(a) The iris 537 

{d) The vitreous body , 538 

(c) The lens 538 

{d) The retina 538 

Conclusions 540 

Acknowledgments 541 

Bibliography 541 



INTRODUCTION. 

This paper is the fourth of a series on the Eyes of Blind 
Vertebrates of North America, and the forty- third contribution 
on zoological topics emanating from the Zoological Laboratory 
of Indiana University. It is one of the reports of a committee 
of the American Association for the Advancement of Science 
on the Investigation of the Cave Fauna of North America, a 
committee of which Theo. N. Gill is chairman, the author se- 
cretary, and A. S. Packard, C. O. Whitman, S. H. Gage, 
and H. C. Bumpus, the other members. The researches on 
which this report is based were assisted by grants from the 
American Association for the Advancement of Science. The* 
three preceding reports on this subject are as follows : 

Proc. Wash. Acad. Sci., Sept., 1902. 533 



534 EIGENMANN 

1889. I. The Eyes of ^/;z3/>^(9/i'/^c5. Arch. f. Entwickelungsmech., 

VIII, pp. 545-617, plates xi-xv. 
1900. II. The Eyes of Typhlomolg-e rathbunz ^tQ^nQgQV. Trans. 

Am. Microsc. Soc, xxi, pp. 49-60, plates iii and iv. 
1900. III. The Structure and Ontogenic Degeneration of the Eyes 

of the Missouri Cave Salamander. Biological Bulletin, 11, pp. 

33-40. plate. 

HABITS OF RHINEURA. 

Rhineura Jloridana Baird is a legless, burrowing, blind Amphis- 
baenian lizard. It is abundant in some parts of Florida. The largest 
individual I secured measured 340 mm. The tail is very short, flat- 
tened dorsoventrally, and the upper surface of its distal half is strongly 
rugose. Each of the transverse rings is here, with numerous tuber- 
cles. The mouth is small; the tip of the lower jaw is some distance 
behind the tip of the upper jaw. In shape, color and arrangement of 
its dermal plates it strikingly resembles an earthworm. This resem- 
blance is heightened by its vermiform progression through the rhythmic 
movements of its annular plates. Its forward and backward locomo- 
tion in its burro^vs is entirely due to this vermiform movement. It 
burrows rapidly, and for this its small, hard, conical head is well 
adapted. The point of the snout is turned down and the head then 
thrust upward in a rooting fashion. An individual will readily disap- 
pear in from half a minute to two minutes. By placing it in a glass 
vessel partly filled ^vith earth its burrowing can readily be seen from 
below. If placed on a bare surface it for a time will Avriggle actively 
from side to side, snake fashion, but without much effect as far as loco- 
motion is concerned. The tail, under such circumstances, is dragged 
behind, as if it had no vital connection with the head. Rarely there 
is a suggestion of a bracing with the tip of the tail against the floor. 
In one minute an individual moved 250 mm. In an attempt at root- 
ing:, after the snout had become \vedged under the edg^e of an immov- 
able object, the whole body to the tip of the tail was repeatedly lifted 
off the floor. 

Rhineura is, as far as I know, one of the two blind vertebrates that 
have been found in the fossil state. Baur described a species of Rhi- 
neura (R. hatcherii) and another Amphisbsenian {^Hypsorhina an- 
tigzia) from the Miocene beds of South Dakota. Baur says nothing 
concerning the dermal plates, so that nothing is definitely known about 
the eyes of this fossil Rhineura. Since all the genera of the family 
Amphisbsenidse have rudimentary eyes, the eyes were verv' probably 
degenerate before the genera became separated. It seems quite cer- 



THE EYES OF RHINEURA FLORIDANA 535 

tain that any fossil members of an existing genus all of whose living 
species have degenerate eyes, must have had eyes that were to a greater 
or less extent degenerate. The time suggested by this find of Baur 
during which the eyes of Rhineura have been degenerating is sur- 
prisingly long, extending as it does through about 5 to 10 percent of 
the formation of sedimentary rocks. This is in distinct contrast to the 
Amblyopsidae, the family of blind fishes, in which the eyes have 
reached their present condition largely since the glacial epoch, during 
which the caves of the Ohio valley were not habitable. The eyes of 
the latter were, however, very probably degenerate to a certain degree 
before they entered the caves. 

Rhineura is a burrowing animal, and blind animals which burrow 
in the ground are not found in naturally made caves. The latter are 
largely populated by species that tend to hide in crevices or natural 
cavities under rocks. It would seem from this that the cave fauna was 
incipient before the existence of caves, and that the latter were colo- 
nized as soon as they were large enough to admit their present inhabi- 
tants.^ 

GENERAL ACCOUNT OF THE EYE. 

The eye of Rhineura Jloridana is not visible externally, nor is 
there any indication where it formerly came to the surface. The side 

1 1 have in divers other places emphasized the fact of the voluntary coloniza- 
tion of caves by animals predisposed to shun the light or creep under rocks or into 
crevices. In other words, the predisposition to become cave animals existed 
before the present caves were formed. There is no doubt whatever that the 
colonizers have been profoundly modified since they entered the caves. Ernest 
Krause (Prometheus, ix, 652) enters the following protest : 

" Well, whoever believes it may also attain blessedness in the belief that caves 
were created to serve as the playground and elysian fields, as it were, of the blind 
of all classes of animals. We have repeatedly heard these siren songs out of the 
mystic darkness of the enemies of light and of the development theory ; they are 
in harmony with the growing effort to upset Lamarckism, Darwinism and even 
Weissmannism, and hence, before we admit the convincing force of Eigenmann's 
conclusions, we must look a little more closely at their foundations." 

Mr. Krause continues for another column to show how very wrong it is not 
to agree with him that the degeneration of the eyes of cave creatures is due to the 
absence of light. It is, however, necessary to get our animals into the caves 
before their eyes may degenerate as the result of the absence of light, and they 
must be able to maintain theinselves in the dark after we have got them there. A 
sudden and accidental colonization is, therefore, out of the question. If species 
depending on their eyes for food are excluded as candidates for cave existence, 
nocturnal animals, negatively heliotropic or positively stereotropic ones, must 
have supplied the present cave fauna. An examination of the inhabitants of any 
cave will readily demonstrate that its fauna was derived from the latter classes 
and that, in spite of the absence of light, many of them have not yet undergone 
any appreciable degeneration as far as their eyes are concerned. 



536 



EIGENMANN 




Fig. 22. Side view of head of 
Rhineura showing surface plates 
and position of eye in relation to 
them. 



of the head is continuously covered w4th plates. There are four 
labials (i, 2, 3 and 4, of fig. 22), the posterior of which is compara- 
tively large. Above the labials from in front backv^rard lie a single 
nasal (5), a single loreal (6), a single preorbital (7), and a group of 
temporals (8). Above this series of plates lie a supranasal (9), joined 
to its fellow of the other side, a prefrontal (11) and two supraciliaries 
(12, 13). In heads cleared with xylol the black eye can be seen to 

lie underneath the angle between the 
two supraciliaries and the preorbital. 
The dermis and epidermis over the 
eye are not different from these struc- 
tures over neighboring regions ex- 
cept that in one instance (PL xxxii, 
fig. 3, df) a solid column of cells 
32 // thick extends from Harder's 
gland to near the epidermis, with- 
out however fusing with the latter. 
Fisher (1900, p. 470) found that in 
Trogofiophis the epidermis is re- 
duced to half its thickness and free 
from pigment over the eye. In Amphisbcena strauchi and A. dar- 
ivini the skin is not thinner and the pigment is little or not at all less 
over the eye. A conjunctival sac has been described for various 
Amphisbasnians. No such structure is present in Rhineura. 

Harder's gland (PI. xxxii, figs. 2 and 3, HGl.) is out of all propor- 
tion to the size of the eye. In a horizontal section it measures about 
four times as long as the eye (medio-laterally) and three times as wide 
(antero-posteriorly) . Duvernoy found that in Typhlops Harder's gland 
is ten times as great as the eye. It is divided into two distinct lobes, 
that over the anterior face of the eye is histologically quite different 
from that over the posterior face. In vertical section the gland is seen 
to entirely surround the eye except sometimes at its lower posterior 
quarter. The large size of Harder's gland has given rise (Duvernoy) 
to the conclusion that its function is not connected with the eye. Its 
secretion is poured directly into the tear duct and through it into the 
nasal cavity. 

The distance of the eye beneath the outer surface of the epidermis 
measures between 320 and 560 microns in specimens between 280 and 
310 mm. long. It is surrounded by t^vo layers of connective tissue. 
These are thin over the distal half of the eye. Over the proximal 
narrow end of the eye they become thick and since they are prolonged 



THE EYES OF RHINEURA FLORIDANA 



537 



beyond the eye, stain a different tint and readily become separated, 
they are easily distinguishable. They probably represent the sclera 
and choroid. If so the choroid is practically free from pigment ex- 
cept possibly in rare instances where a few pigment granules were 
detected in cells closely applied to the eye. There is no indication of 
any differentiation into a cornea or capsule of any sort. The fibrous 
sheaths are at the proximal end drawn out into a cone. A supposed 
scleral cartilage has been found in one individual. Here a bar about 
20 /Jt thick extends from over the center of the distal face of the eye 
for 160 [1 around its posterior face. It stains and has the structure of 
bone rather than of cartilage. 

No traces of any muscles have been found connected with the 
eye. 

The eye is directed outward and forward. Its axis is horizontal and 
makes an angle of about 60° with the sagittal plane of the body. It 
does not occupy a definitely fixed position on its axis. In the eye of 
one side the choroid fissure was found directed caudad, in the other 
eye ventrad. It is irregularly pear-shaped, w^ith its anterior face con- 
vex, its posterior face flat or even concave. The eyes in three speci 
mens give the following measurements in microns : 

MEASUREMENTS IN MICRONS OF EYES OF RhINEURA. 



Length of 

Specimen. 

Millim. 


Medio-lateral Diameter. 


Antero-posterior Diam. 


Distance from Surface. 


Left Eye. 


Right Eye. 


Left Eye. 


Right Eye. 


Left Eye. 


Right Eye. 


275 

280 

310 


320 
312 
320 


320 
298 
320 


128 
160 
216 


176 
i8r 
176 


480 
320 
560 


336 
368 
560 



MINUTE ANATOMY OF THE EYE. 

All the structures vary greatly in different eyes so that the terms 
''sometimes,'* ''usually," frequently," etc., have to be used much 
more than is desirable. This cannot be avoided unless each eye is 
given a distinct description. 

(a:) The Iris. — In the structure of the irideal region the eye of this 
species is unique among the degenerate vertebrate eyes so far described. 
In all other eyes, with the possible exception of Trog'ltchthys^ elements 
of an iris are distinctly recognizable. In Rhineura the fold of double 
epithelium between the pigmented and unpigmented part of the retina 
whose margin is the margin of the pupil has been obliterated and the 
pupillary edge forms the extreme outer edge of the blunt end of the 
pear (PI. xxxiii, fig. i, /). The pigmented layer of the retina in 



538 EIGENMANN 

Other words merges directly iuto the unpigraented layers of the retina. 
The entire thickness of the retina is thus exposed at the distal face of 
the eye. 

(3) The Vitreous Body. — The vitreous cavit}' is represented bv a 
vertical slit extending from the axis of the eve downward to the edsfe. 
The choroid fissure (PL xxxiv. fig. 4, Chr.f.^ thus remains perma- 
nently open in so far as the edges of the opposite sides of the fissure 
are not united. In one eye a space a fe^v microns ^vide was found in 
the eye. In other cases there is no real cavit}- and no vitreous body. 
The hyaloid membrane (PL xxxiii. fig. i and PL xxxiv, fig. 4. hd^ is 
represented by a few cells -with elongated nuclei. Blood vessels were 
not found in it. 

(c) The Lens. — In two specimens no traces of a lens were found. 
In t^vo other specimens a lens ^vas present. There being no pupil and 
no vitreous cavit}' the lens is situated in a little depression in the distal 
face of the retina (PL xxxii, fig. 4 : PL xxxiv. figs. 1.2,3). '^^^ lenses 
differ gi'eatly from each other. In the better developed instances (PL 
xxxiv, fig. i) it is composed of a spherical mass of cells. The nuclei 
are granular and are surrounded by a hyaline cell body. These little 
capsules are closely packed in a slightly darker matrix. The whole lens 
is surrounded by a fibrous capsule containing elongated nuclei. Both 
eves of one individual are provided with lenses as described. In another 
individual the t^vo lenses differ materially not only from those 
described, but from each other both in structure and size. The left 
lens consists of a lenticular nodule containing: about six dense nuclei 
(PL XXXIV, fig. 2). On the right side (PL xxxiv, fig. 3) the lens is 
much larger. It consists of t^vo large nucleated capsules surrounded 
by a matrix containing a few dense elongated nuclei similar to those of 
the capsule surrounding it (PL xxxiv, figs, i, 2, 3 are drawn to the 
same scale) . The difference exclusive of size bet\veen the two cap- 
sules and the many nuclei represented in PL xxxiv, fig. i, may be due 
to differences in the method of preparation. 

(^) The Retina. — The numbers in the following paragraphs are 
not consecutive, but are those used to designate the corresponding 
lajers in the figures. 

I. The pigment epithelium forms a complete outer layer of the eye 
exclusive of its distal face and a narrow strip along the choroid fissure. 
The extent to which this epithelium is pigmented differs greatly in 
different eves. A region along either side of the choroid fissure is 
free from pigment, occasionally parts of the anterior face of the eye 
are free from pigment (PL xxxiii, fig. 2) and verj,- frequently the 



THE EYES OF RHINEURA FLORIDANA 539 

cells of this layer around the distal margin of the eye are free from 
pigment. Over the anterior face of the eye this layer is usually com- 
posed of a regular layer of cells whether these are free from pigment 
or not (PL xxxiii, figs, i and 2). On the posterior face the series of 
cells is not nearly so regular. The pigmented epithelium is here in- 
vaginated and folded upon itself in various v^^ays. The infoldings are 
sometimes solid masses of pigment cells, but sometimes they form 
hollow^ spheres which contain a mass of concentrically arranged un- 
pigmented material, probably of choroidal origin (PI. xxxii, fig. 6c and 
PI. XXXIII, fig. 3). What the significance of these cysts may be I 
cannot conjecture. Indications of similar structures were in these ne 
eyes of Amblyopsis. 

The narrow stalk of the pear-shaped eye is usually filled with an 
irregular jumble of pigment cells. In favorable sections it is seen that 
these are also the result of an invagination of the pigment epithelium 
from the pointed end of the eye (PI. xxxiii, fig. 2). The pigment 
epithelium has not been reduced at the same rate as the rest of the 
retina ; as a consequence it is infolded in various ways. Small pig- 
ment cells are sometimes found in the inner layers of the retina among 
the ganglionic cells and along the optic nerve within the eye. Pigment 
cells were also found in the eyes of Typhlomolge (Eigenmann, 1900, 
figs. 2 and 6, 2r). There are rarely any pigment cells over the distal 
face of the eye. 

\a, X^ nuclei. In the eyes of Typhlichthys (Eigenmann, 1899, 
fig. 44, ^, and Troglichthys^ figs. 52 and 56, nl') I described a 
few cells with elongated tangentially placed nuclei between the pig- 
mented epithelium and the outer nuclear layer. I was unable to account 
for these in the eyes of the two fishes mentioned. Similar cells, 
similarly located, are present in this eye. They are distinctly outside 
of the outer limiting membrane (PI. xxxii, fig. 5 ; PL xxxiii, figs. 
I, 2). I am at as great a loss to explain the origin of these nuclei 
as I was those found in Typhlichthys. Possibly they are derived from 
the pigment epithelium which in some of the unpigmented regions 
(PL xxxiii, fig. 2, x) are more than one layer deep. If the outer 
layer should become pigmented the inner nuclei if they remained unpig- 
mented might give rise to these longitudinal cells. 

2. Rods and cones are not present. There is in some cases a distinct 
space between the pigment epithelium and the outer nuclear layer. 
This space when present is partially filled with filmy, hazy structures, 
but nothing suggesting definitely either a rod or cone was detected 
(PL XXXII, fig. 5 ; PL xxxiii, fig. i). 



$40 EIGENMANN 

3. The outer nuclear layer consists of about two series of elliptical 
nuclei. They form a compact and distinct layer a few microns from 
the outer limiting membrane (PL xxxii, fig. 5 ; PI. xxxiii, figs. 1,2; 
PL XXXIV, fig. 4). 

4. The outer reticular layer is represented by a series of distinct but 
irregular gaps between the outer nuclei and the inner nuclei. Hori- 
zontal cells are not present (PL xxxii, fig. 5 ; PL xxxiii, figs, i, 2, 3). 

6. The inner nuclei are smaller, rounded and less granular than the 
outer nuclei. They do not form as compact a layer as the outer nuclei. 
It is impossible to distinguish between bipolar and spongioblastic cells 
(6 in the different figures). 

8. As is usual with the inner reticular layers in degenerate eyes this 
layer is \vell developed in the eyes of Rhineura. It is frequently 
crossed by Miillerian fibers (8 in the figures). 

9. The ganglionic layer is represented by a number of nuclei loosely 
grouped about the vitreous slit. The individual nuclei are distinctly 
larger than those of the inner nuclear layer and less oval than those of 
the outer nuclear layer (9 in the figures) . 

10. A distinct optic fiber layer is not present and the optic nerve is 
no\vhere within the eye a compact strand of fibers. A loose flocculent 
strand of fibers passes through the proximal part of the retina. Its 
path through the pigmented layer is difficult to trace. Beyond the eye 
the optic ner\-e can be followed in my preparations by means of the 
fibrous sheaths and pigment cells associated with it (PL xxxiii, fig. 4) 
rather than by the presence of any fibers with a distinctly nervous 
structure. The optic nerve leaves the eye not at the proximal end or 
the narrow end of the pear but anterior to the pigment mass in the 
narrow^ part of the pear (PL xxxiii, fig. 2, n. op.'). 

CONCLUSIONS. 

1. The eye of Rhineura has reached its present stage as the result 
of a process of degeneration that probably began in the early Miocene. 

2. The dermis and epidermis pass over the eye without any modifi- 
cations. The conjunctival pocket has vanished. 

3. Harder's gland is many times as large as the eye and pours its 
secretion into the tear duct and thus into the nasal cavity. 

4. The eye muscles have disappeared. 

5. A cornea is not differentiated. 

6. The lens is absent in half the eyes examined and varies greatly 
in those in which it is present. 

7. The vitreous body has practically disappeared. 



THE EYES OF RHINEURA FLORIDANA 54I 

8. The pigment epithelium is variously pigmented. It is of greater 
extent than is sufficient to cover the retina and has been variously in- 
vaginated or puckered over the proximal and posterior faces of the eye. 

9. An uveal part of the iris is not present. 

10. The eye of Rhineura does not represent a phylogenetically 
primitive stage ; it is an end product of evolution as truly as the most 
highly developed eye.^ 

1 1 . The adult eye shows few indications that there has been a ces- 
sation of development at any definite ontogenic stage. It does not re- 
semble as a whole any ontogenic stage. 

12. An arrest in the ontogenic development has taken place in so 
far as the number of cell multiplications concerned in forming the an- 
lage of the various parts of the eye have decreased in number, and in 
the lack of union of the lips of the choroid fissure. 

13. It is possible that the absence of cones or rods is due to an arrest 
in the histogenesis of the retina but since these structures are normally 
formed in the young of Typhlotriton and disappear with age it is 
possible that their absence in the adult eye of Rhineura is also due to 
ontogenic degeneration. 

14. The irregularity in the structure and existence of the lens and 
the great reduction of the vitreous body offer evidence in favor of the 
idea of the ontogenically and phylogenically earlier disappearance of 
the ontogenically and phylogenically newer structures. 

15. Horizontal nuclei found between the pigment epithelium and 
the outer limiting membrane are probably derived from the proximal 
layer of the optic cup. 

16. The different layers of the retina have reached a degree of dif- 
ferentiation out of proportion to the great reduction of the dioptric 
apparatus and general structure of the eye. 

ACKNOWLEDGMENTS . 

My attention was called to this lizard by Mr. W. S. Blatchley, State 

geologist of Indiana. Dr. W. B. Fletcher, of Indianapolis, kindly 

secured some specimens for me. To both of these gentlemen I wish 

to express my obligations. Other specimens were secured through 

dealers. 

BIBLIOGRAPHY. 

List of papers bearing on the eyes of the Amphisbsenians. 
Baur, George. 
1893 The Discovery of Miocene Amphisbsenians. Am. Nat., 1893, p. 998. 

^The detailed considerations on which conclusions 10, 11, 12, 14 are based are 
not presented in the body of this paper. They will, however, be granted no 
doubt. 



542 EIGENMANN 

Bora, G.i 

1876 and 1879 Ueber die Nasenholen und den Thranenausgang der Amphibian. 
Morphologisches Jahrbuch, 11, 1876, and v, 1S79. 
Boulenger, G. A. 

1885 Catalogue of Lizards, 2d edition. Vol. 11, p. 430. 

Cope, E. D. 

1898 The Crocodilians, Lizards and Snakes of North America. Smithsonian 
Report. U. S. Nat. Mus., 1898, pp. 682-6S8. 
Denburgh, John van. 

1897 The Reptiles of the Pacific Coast and Great Basin. Occasional papers 
Cal. Acad. Sci., v. 1897. 

Fischer, E. 

Beitr. z. Kenntniss d. Nasenhohle u. d. Thranennasenganges d. Am- 
phisbaeniden. Arch. Mikr. Anat., SS^ PP- 44i~4785 Pis. xxi-xxiv. 

Hoffmann, C. K. 

1884 Bronn's Klassen und Ordnungen des Thierreiches, vi, 3, p. 799. 

Kohl, C.i 

1892 Rudimentare Wirbelthieraugen. Bibl. Zool., Heft 13. 

Stannius, H.^ 

1895 Handbuch der Zootomie. Berlin, 1859. 
1 Not seen by the author of this paper. 



NOTZ.— .^ 



Fk 



PLATE XXXII. 



rrand of cells 



During extent of pig- 



eye. 

Horizontal sec:: :" :: e:: t; t :: -::^~r ::m: :;u 

mentation ar. z t r. . 
Distal part of a: : : r. er section of same eye showing the different layers 

of tl^ retina .: their highest development. 2 -.-. , -bjective. 
Proximal part of ar. ;:r.er e e showing the : -t retT erttd diagrammat- 



icallv in PL xxxiii. h^. 



2 mm. o: 



EXPLAXATIOX OF XOTATIIN" 



I. Pigment epitheliun:!. 

3. Outer nuclear layer. 

4. Outer reticular layer. 
6. Inner nuclear layer. 

8. Inner reticolar layer. 

9. Ganglionic layer. 

c. Cyst of pigment cells containing 

pigmentless material. 
chr. Choroid. 
ckr.f. CluHt>idal fissure. 
cfs. Blood corpuscles. 
D. Dorsad. 



H. g:. 

id. Ky 



j.ar.a. 



r...-f. Op tic nerve. 
/. Mr^-iir. of pupil. 
i?. Dex^rao. 
scl. Sclera- 
Fl Ventrad. 

X. Flattened ceUs beneath the pigment 
epithelium. 

(544) 



pROC. Wash. Acad. Sci. Vol, IV, 



Plate XXXI 




From photographs. 



EYES OF RHINEURA FLORIDANA. 



PLATE XXXIII. 



Note. — ^AU figures were drawn with camera lucida from sections mounted in 
balsam. The horizontal sections were made from above down and are so drawn 
that the anterior face of the figure is toward the top of the page. 
Fig. I. Horizontal section of left eye of a specimen 280 mm. long, 2 mm. objec- 
tive and 4 eye piece. 

2. Another section through same eye showing exit of the optic nerve, the 

pigmentless condition over the anterior face of the eye and the invagi- 
nated pigment at the end of the pear. 2 mm. objective and 4 eye piece. 

3. Outline of pigment in the proximal end of right eye of the same indi- 

vidual showing the invagination of the pigment to form a cyst. 2 mm. 
objective and 4 eye piece. 

4. Part of optic nerve of right eye of an individual 275 mm. long with its 

pigment cells, just beyond the eye. 2 mm. objective and 4 eye piece. 

Explanation of Notation Used. 



I. Pigment epithelium. 

3. Outer nuclear layer. 

4. Outer reticular layer. 
6. Inner nuclear layer. 

8. Inner reticular layer. 

9. Ganglionic layer. 

c. Cyst of pigment cells 
pigmentless material. 
c/ir. Choroid. 
chr.f. Choroidal fissure. 
cfr. Blood corpuscles. 
D. Dorsad. 



dt. Solid duct of Harder's gland. 
H. Gl. Harder's gland. 
kd. Hyaloid membrane. 
L. Sinistrad. 
lens. Lens. 
n.of. Optic nerve, 
containing /. Margin of pupil. 
R. Dextrad. 
scl. Sclera. 
V. Ventrad. 

X. Flattened cells beneath the pigment 
epithelium. 

(546) 



Proc. Wash. Acad. Sci. Vol. IV 



Plate XXXIII 





C. H. E. DEL. 



EYES OF RHINEURA FLORIDANA. 



A.e.^Mit'}!'! UTH WA-iH.D-C. 



PLATE XXXIV. 

Note. — All figures were drawn with camera lucida from sections mounted in 
balsam. The horizontal sections were made from above down and are so drawn 
that the anterior face of the figure is toward the top of the page. 
Fig. I. Vertical section through distal part of an eye showing the lens with its 
capsule. 2 mm. objective and 4 eye piece. 

2. Lens of left eye of the individual 275 mm. long from which fig. i (PL 

xxxiii) and fig. 22 are taken. Horizontal section, 2 mm. objective 
and 4 eye piece. 

3. Right lens of same individual under the same magnification. 

4. Sagittal section through middle of left eye of an individual about 300 mm. 

long. 2 mm. objective and 4 eye piece. 



Explanation of 

I. Pigment epithelium. 

3. Outer nuclear layer. 

4. Outer reticular layer. 
6. Inner nuclear layer. 

8. Inner reticular layer. 

9. Ganglionic layer. 

c. Cyst of pigment cells containing 

pigmentless material. 
c^r. Choroid. 
ckr.f. Choroidal fissure. 
cpr. Blood corpuscles.' 
D. Dorsad. 



Notation Used. 

dt. Solid duct of Harder's gland. 
H.Gl. Harder's gland. 
Jid. Hyaloid membrane. 
L. Sinistrad. 
lens. Lens. 
n.op. Optic nerve. 
^. Margin of pupil. 
R. Dextrad. 
scl. Sclera. 
V. Ventrad. 

X. Flattened cells beneath the pigment 
epithelium. 

(548) 



Proc. Wash. Acad. Sci. Vol. IV 



Plate XXXIV 



I 



I 




, — lem 



\ 



6.. ^vv:-:- ^W?<: 



-A \ 



9 ~ 



JL 



lens 





C. H. E. DEL. 



EYES OF RHINEURA FLORIDANA. 



A.e.immfi lith. mm d.c. 



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